The brightness and color of a physical light depend upon other lights seem before or at the same time. This research will investigate the mechanisms by which one light can affect the perceived color and brightness of another. The research program has two related parts. First, mechanisms of visual adaptation affecting the color of a monocularly presented light will be further investigated. Previous research has revealed two distinct mechanisms affect color perception: receptor sensitivity change and a chromatically opponent "restoring effect" that tends to counterbalance the influence of adapting-field quanta that fall in the area of the incremental test field. This research will investigate the spatial, temporal, and wavelength-dependent properties of the restoring effect, and attempt to relate them to chromatically opponent mechanisms that affect threshold detection. The second part of the research program will examine the nature and locus of other mechanisms affecting brightness and color perception. Relatively little is known about effects of adaptation on mechanisms influenced by signals from both eyes. These mechanisms will be explored with haploscopic experiments; a formal approach leading to specific hypotheses will be used since incorrect inferences from haploscopic experiments are common. The hypotheses to be tested concern the effect of light presented to one eye on the percept due to light entering the other eye. These experiments can reveal a role of central mechanisms in visual adaptation. This research will evaluate effects due to various mechanisms of adaptation on suprathreshold brightness and color perception. Because effects of adaptation sometimes are more obvious for brightness and color perception than for threshold detection, the results of this work can lead to new and improved psychophysical methods for evaluating the locus and nature of mechanisms resulting in abnormal vision. A long-term goal of this research is to provide sensitive and reliable psychophysical techniques for the diagnosis of eye disorders.